Compared with solvent based silicone PSA, emulsion type silicone PSA is very attractive from safety and environment perspectives. However limited public reports were found in the prior art.
For example, JP 3516410 (Patent Reference 1, incorporated herein for reference) reported Pt or peroxide cured PSA emulsion. In the embodiments thereof, silicone PSA composition was heat bodied and the solvent was then removed. The following emulsification was carried out with traditional organic surfactant. However, the catalyst needed emulsifying with PSA composition just before use which was actually inconvenient for practical use.
For example, JP 4761049 (Patent Reference 2, incorporated herein for reference) prepared the emulsion of each PSA component (e.g. diorganopolysiloxane) emulsion and resin emulsion and mixed together to get final PSA emulsion. Although peroxide catalyst emulsion was directly used in this patent, the stability or availability of peroxide emulsion was a doubt.
For example, CN 101177596 (Patent Reference 3, incorporated herein for reference) also reported a silicone PSA emulsion composed of MQ resin emulsion, silicone gum emulsion, silane and organic tin catalyst. However, this patent emphasizes the use of organic tin catalyst, which is not preferred because of environmental reasons. The process described was also complex and limited the formulation freedom.
For example, U.S. Pat. No. 6,545,086 (Patent Reference 4, incorporated herein for reference) reported a silicone PSA emulsion prepared by dispersing PSA composition in volatile silicone fluid and emulsifying with surfactant. It also mentioned the method to reduce volatile content. However, with traditional organic surfactants the reported particle size of the emulsion was big and also there was no performance data to support its use as PSA.
Therefore, there still exists a need in the art for obtaining practically useful, safe and environmentally-friendly emulsion type silicone pressure sensitive adhesive which has small particle size, good appearance, stability and peel adhesion, and, compared with peroxide curing of the prior art, the obtained PSA emulsion can be directly mixed with amino silane or platinum emulsion just before use without necessity for pre-emulsifying.